Wind turbines are arranged to capture energy of the wind by means of one or more rotor blades, and to transfer this energy into electrical energy by means of a generator. In some wind turbines, a drive train, including a gear arrangement, is provided for transferring rotational movements of a hub carrying the rotor blade(s) to rotational movements of the generator. The gear arrangement may comprise a number of intermeshed toothed gear wheels which provides an appropriate gearing between the rotational movements of the hub and the rotational movements of the generator shaft. As an alternative, the gear arrangement may comprise a number of pulleys being interconnected by means of a number of belts or chains, in order to transfer rotational movements between the pulleys.
To use a belt to transmit the rotation from the rotor to a generator is known from, among others, WO2015/058770A1. In order to prevent ratcheting or tooth jump, a toothed belt is installed with a preload or tension. The preload must be large enough such that the belt will not jump on the sprocket during full load operation. The preload tension is applied during installation. The preload tension can be a significant source of belt wear and noise. Improper or lack of preload may also cause tooth cracking. It can also diminish system efficiency. Preload for a toothed belt can be over 100 pounds depending belt pitch and width, see Wallace Erickson, Belt Selection and Application for Engineers 277-299, Marcel Dekker, Inc. (1987).
The prior art relies on a simple routing of the drive belts. Improper allocation of belt tension, routing and alignment will reduce the operational life of a drive belt representing significant cost to repair or replace. It will also reduce the overall efficiency of the turbine drive system, also representing increased costs.
Representative of the art is EP2391825 which discloses a drive device for a windmill comprising a large pulley disposed on a main shaft and at least one belt or chain adapted to transfer rotation from the pulley to a generator. The pulley is rotationally coupled to at least two secondary shafts which are disposed parallel to the main shaft. One or more belts which transfer the rotation, extend over the pulley and the secondary shafts. The secondary shafts are in turn rotationally coupled to at least one, preferably two, electric generators.
What is needed is a belt drive mechanism comprising a first flexible member and a second flexible member each having at least one segment with a tensile load of approximately zero newtons during operation. The present invention meets this need.